Military aircraft are powered by engines which generate heat that produces hot metal surfaces within the engine as well as a stream of heated exhaust gases. These sources of infra-red radiation, i.e., the hot metal engine surfaces and the stream of heated exhaust gas, provide a target source for heat-seeking missiles which can lock on the target source and be led to the aircraft.
To provide a military aircraft with a power source which is not easily discernible by a heat-seeking missile, a first step would be to insulate the surfaces of the aircraft engine. An insulation material which is well suited for this purpose is disclosed in U.S. Pat. Nos. 4,037,751 and 3,948,295.
The insulation of the aircraft engine surfaces does not, however, prevent viewing of the engine by a heat-seeking missile. Even when the aircraft engine is well insulated, hot metal surfaces within the engine interior may still be viewed by a heat-seeking missile through an opening for exhaust gases positioned adjacent to the hot interior surfaces. In addition to insulating the exterior surface of the engine, it is, therefore, also necessary to block the hot surfaces within the engine interior from being viewed through the exhaust gas opening. Additionally, it is necessary to reduce infra-red radiation from the hot plume of exhaust gases that is emitted by the aircraft engine such that the exhaust gases cannot be readily detected by a heat-seeking missile.
The device disclosed in my prior U.S. Pat. No. 3,930,627 serves to prevent the detection of an aircraft by a heat-seeking missile by providing an exhaust gas-conducting member that is adapted to receive heated exhaust gases from an exhaust opening of an aircraft engine. The device of my prior patent provides a configuration which blocks the exhaust opening of the engine from line-of-sight view through the outlet of the exhaust gas-conducting member. Additionally, the device of my prior patent functions to reduce infra-red radiation from exhaust gases emitted by the aircraft engine by breaking up the stream of exhaust gas into a plurality of smaller streams and mixing cooling air with the heated exhaust gases.
In accomplishing these beneficial results, the device of my prior U.S. Pat. No. 3,930,627 employs cooling air which is received by an air intake which leads to the interior of the gas conducting member. The cooling air is received by the device of my prior patent as the aircraft moves the device through the air. Additionally, airflow may be generated by the propeller or rotor that is driven by the aircraft engine, with the airflow being received by the air intake and conveyed to the interior of the gas-conducting member. The airspeed of a military aircraft, particularly a helicopter, will not be constant. As a result, the quantity of cooling air received by the gas-conducting member in the device of my prior patent will vary during the operation of the aircraft. This variation in the quantity of cooling air may produce variations in the heat content of the exhaust gases from the exhaust gas member. Also, there may be some degree of fluctuation in the temperature of the exhaust gas member in my prior device. In a hovering helicopter having an airspeed of zero, the exhaust gases discharged from the gas-conducting member in my prior device may experience a rapid temperature increase such that the gases become visible to infra-red detection. This could be disastrous and result in the loss of the aircraft to a heat-seeking missile.
In view of the possible fluctuations in the operation of the device of my prior patent, U.S. Pat. No. 3,930,627, in response to changes in the airspeed of the host aircraft, a radiation shielding device would be desirable whose operation would be less dependent upon the airspeed of the host vehicle. This would permit the radiation shielding device to operate efficiently even when the vehicle had an airspeed of zero, as in the case of a hovering helicopter. Also, this would permit the use of the radiation shielding device on a stationary power source in shielding the power source from detection by a heat-seeking missile.